<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Title</title>
  </head>
  <body>
    <h1>hello</h1>
    <form action="/demo">
      <input type="text" name="num1" value="10"><br><br>
      <input type="text" name="num2" value="20"><br><br>
      <button type="submit">计算</button>
    </form>
  </body>
</html>